As sizes of transistors are reduced, a thin film such as an insulating film constituting a sidewall spacer (SWS) of a gate electrode requires a low temperature for film forming, an improved resistance to hydrogen fluoride (HF), and a low dielectric constant. Thus, it is researched to employ as the insulating film a silicon boronitride film (SiBN film) in which boron (B) is added to a silicon nitride film (SiN film) or a silicon borocarbonitride film (SiBCN film) in which carbon (C) is also added.
Since such an insulating film as described above requires high step coverage properties, it may be often formed by an alternate supply method of alternately supplying different kinds of processing gases. For example, dichlorosilane (SiH2Cl2) gas or the like which is a silicon-containing gas as a silicon source, boron trichloride (BCl3) gas, diborane (B2H6) gas or the like as a boron source, ammonia (NH3) gas or the like as a nitrogen source, and ethylene (C2H4) gas, propylene (C3H6) gas or the like as a carbon source may be used so that a cycle of sequentially supplying those processing gases to a substrate is performed a predetermined number of times so as to form a SiBN or SiBCN film on the substrate. However, in the above method separately supplying the silicon source, the boron source, the nitrogen source, and the carbon source, the productivity for film forming may be deteriorated due to an extended time required for each cycle.